Arsenal need only a point from their last two games to qualify but that late collapse has wrecked their hopes of finishing above Borussia Dortmund at the top of Group D.

The groups have still to be settled, of course, but it is seemingly inevitable that Arsenal will be on the opposite half of the draw to Real Madrid, Bayern Munich, Atletico Madrid and either Paris St Germain or Barcelona.

Porto or Bayer Leverkusen is the best Arsenal can hope for, but if they defend like they did against Anderlecht, those two will have enough to beat them too.

We have to defend better as a team

Per Mertesacker

It will be the fifth season running this has happened - admittedly once after winning the group and drawing a potent AC Milan - and the result has always been the same. Elimination. Defender Mertesacker says it is not good enough.

"It is going to be the same things as last year and the year before where we finished second and the draw gave us Munich," he said. "That is up to us, we did that. It was due this time to lack of defending.

"We didn't stop Anderlecht playing and they are good at it. When you don't give them pressure they can deliver good balls through the middle. They can cause trouble and we just left them playing and that was the problem.

"We have to defend better as a team. Even when we dropped deeper they always looked dangerous.

"Everyone has to be involved to defend. We cannot afford that we have just five or six players defending and just the back four. That's what we lacked especially in the final third in the last 20 minutes.

"It was a good warning and that everyone should raise their game and give 10 per cent more when it is really needed."

Mertesacker then used a phrase that has become quite familiar to Arsenal in recent seasons: "We'll bounce back quickly."

It always follows either a shock or heavy defeat. And to be fair, Arsenal do have that bouncebackability to respond to humiliations with their own form of flat-track bullying by beating smaller clubs in the games that follow, so Swansea beware on Sunday.

But that masks the issue that against quality sides they rarely deliver, and remember they are only on course to finish above Anderlecht because they snatched an unlikely victory with two late goals after being outplayed in Belgium.

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Arsenal look set to finish second in their Champions League group

Arsenal have paid a heavy price for not replacing Thomas Vermaelen in the summer, meaning they had to play left-back Nacho Monreal in central defence against Anderlecht with Laurent Koscielny injured. Wenger also failed to recruit a quality defensive midfielder and for all the brilliance and goals of Alexis Sanchez, this leaves them vulnerable.

Anderlecht recognised this and delivered another poke at Arsene Wenger's side by saying they were looking only at keeping the score respectable before they were surprisingly allowed back into the game Anderlecht captain, and keeper Silvio Proto said: "At 2-0 down I spoke with our defenders and said we should just shut up shop for the night. Then we conceded a third goal.

"But our confidence came back after we made it 3-1. Arsenal's team is worth many millions of pounds, yet we stood up to them with our young squad. I'm proud of them."

"We started thinking about damage limitation when it went to 2-0," said Vanden Borre. "But when we scored to make it 3-1, we had more and more space. We started to grow in confidence. It went to 3-2 and then 3-3 and Arsenal continued to play.

"It was surprising that they kept playing but all the better for us. It allowed us to come back into the game."

Anderlecht's passionate supporters roared on their team after the first goal, while Arsenal fans went into a stunned silence, just days after Chelsea boss Jose Mourinho criticised his team's fans for making Stamford Bridge too quiet.

Vanden Borre said: "It is like we were playing at home, our supporters are exceptional. They really help us and push us on."

And youngster Andy Kawaya added: "Even when we were 3-0 down, they continued to sing. That is what pushed us - we didn't want to disappoint these supporters. They came in force and we didn't want to let them down. If they are here, we must give ourselves until the last minute."